I just ran into this issue and wrote a separate function to solve this problem.
Inside /wp-content/plugins/glue-for-yoast-seo-amp/classes/class-frontend.php do this:
1. Find public function __construct() and add the following line under the other add_action :
add_action( ‘amp_post_template_head’, array( $this, ‘fix_amp_post_metadesc’ ) );
2. Add the following after the __construct closing bracket }
public function fix_amp_post_metadesc() {
$this->front = WPSEO_Frontend::get_instance();
$desc = $this->front->metadesc( false );
if ( $desc ) {
echo ‘<meta name=”description” content=”‘. $desc .'”/>’;
}
}
3. Done! Amp pages should have their meta descriptions.